1. Field of the Invention
The present invention relates to a drum type weft inserting device for shuttleless looms and, more particularly, to techniques for automatically controlling the weft detaining timing of a weft detaining pin.
2. Description of Related Art
In a drum type weft inserting device, a rotary yarn guide draws out a weft from a yarn package and winds the weft around the outer circumference of a stationary measuring and reserving drum to measure and reserve the weft having a length sufficient for one weft insertion cycle, and a weft detaining pin is moved toward and away from the drum to detain the weft on the outer circumference of the drum and to release the weft wound on the drum for weft insertion, respectively. Upon the release of the weft from the detaiing pin, a picking nozzle spouts a pressurized fluid along the shuttle path into the shed to insert the weft having a measured length into the shed.
Rotative driving means for driving the rotary yarn guide and reciprocative driving means for advancing and retracting the detaining pin, such a cam mechanism, are interlocked mechanically with the crankshaft of the loom in order to operate the rotary yarn guide and the detaining pin synchronously with the principal motion of the loom.
In sequentially inserting a plurality of different wefts by using a plurality of weft inserting device, the detaining pins need to cease from motion sequentially at regular or irregular intervals according to the sequence of insertion of the different wefts, which requires intermittent disconnection of the detaining pins from the cyclic principal motion of the loom. However, the mechanical interlocking means is unable to disconnect the detaining pins intermittently or at irregular intervals, so that optional weft insertion is impossible. Moreover, since the reciprocating speed of the mechanically controlled detaining pin is limited, the reciprocation of the detaining pin becomes unstable when the loom is operated at a high speed.
Such a problem can be solved by driving the rotary yarn guide by an individual motor and by driving the detaining pin by an individual driving device, such as an electromagnetic device, instead of driving the rotary yarn guide and the detaining pin by the crankshaft of the loom through a mechanical interlocking mechanism.
In practical weaving operation, however, the weft inserting speed varies due to the variation of the related factors, such as the tension of the weft in winding the same on the measuring drum. Therefore, the length of the inserted wefts varies when the timing of reciprocation of the detaining pin is fixed.
A weft clamp controller to prevent the insertion of wefts having an excessive or deficient length is disclosed in Unexamined Japanese Patent Publication No. 57-29640. This weft clamp controller controls a weft clamp on the basis of the actual length of the weft unwound from the measuring drum detected by an optical sensor provided on the measuring drm. This invention is very effective only if the optical sensor functions correctly. However, the weft passes the optical sensor in a very short time and the optical sensor is liable to malfunction when waste flies across the optical sensor or when intensive external light enters the optical sensor. Consequently, incomplete or unstable weft insertion results.